You should read the site rules and guidelines for posting videos and also for posting items for sale. It's all covered here in the site rules:
I'm assuming you are referring to marketing/selling dulcimers. There are only two locations you can sell or market items here in FOTMD- either in the For Sale forum (while following its guidelines), or by purchasing a slideshow Ad in the Main Page sponsor showcase. You cannot market a dulcimer for sale through posting a video here. Selling and marketing is confined to the For Sale Forum and to the Ad Slideshow. Hope this answers your question.
Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990